1. Field of the Invention
The present invention relates to replacement valves for improving the cardiac function of a patient suffering from cardiac valve dysfunction, such as aortic valve regurgitation or aortic stenosis. More particularly, the present invention relates to heart valve prostheses that provide improved durability and are particularly well-suited for percutaneous delivery.
2. Background of the Invention
Heart valve replacement has become a routine surgical procedure for patients suffering from valve regurgitation or stenotic calcification of the leaflets. While certain procedures may be performed using minimally-invasive techniques (so-called “keyhole” techniques), the vast majority of valve replacements entail full sternotomy and placing the patient on cardiopulmonary bypass. Traditional open surgery inflicts significant patient trauma and discomfort, requires extensive recuperation times and may result in life-threatening complications.
To address these concerns, within the last decade efforts have been made to perform cardiac valve replacements using minimally-invasive techniques. In these methods, laparascopic instruments are employed to make small openings through the patient's ribs to provide access to the heart. While considerable effort has been devoted to such techniques, widespread acceptance has been limited by the clinician's ability to access only certain regions of the heart using laparoscopic instruments.
Still other efforts have been focused on percutaneous transluminal delivery of replacement cardiac valves to solve the problems presented by traditional open surgery and minimally-invasive surgical methods. In such methods; a valve prosthesis is compacted for delivery in a catheter and then advanced, for example, through an opening in the femoral artery and through the descending aorta to the heart, where the prosthesis then is deployed in the aortic valve annulus. Although transluminal techniques have attained widespread acceptance with respect to delivery of stents to restore vessel patency, only mixed results have been obtained with respect to percutaneous delivery of relatively more complicated valve prostheses.
One such example of a previously-known device heart valve prosthesis is described in U.S. Pat. No. 6,454,799 to Schreck. The prosthesis described in that patent comprises a fabric-based heart valve disposed within a plastically deformable wire-mesh base, and is delivered via expansion of a balloon catheter. One drawback with balloon catheter delivery of the prosthetic valve is that the valve leaflets may be damaged when compressed between the balloon and the base during deployment. In addition, because balloon expandable structures tend to experience some recoil following balloon deflation, perivalvular leaks may develop around the circumference of the valve prosthesis.
Accordingly it would be desirable to provide a percutaneously-deliverable valve prosthesis that reduces the risk of leaflet damage during deployment of the prosthesis. It further would be. desirable to provide a valve prosthesis that reduces the risk of perivalvular leaks resulting from recoil of the prosthesis following deployment.
U.S. Pat. No. 6,027,525 to Suh, et al. describes a valve prosthesis comprising a series of self-expanding units affixed to a polymeric cover and having a valve disposed therein. Such devices are not suitable for cardiac valve replacement because of the limited ability to compact the valve disposed within the prosthesis. Moreover, such valve prostheses would be particularly undesirable for treating aortic valve defects, because the polymeric cover would obscure the ostia of the coronary arteries, both disrupting blood flow to the coronary arteries and preventing subsequent catheterization of those arteries. Accordingly, it would be desirable to provide a valve prosthesis that is self-expanding, yet permits the valve to be compacted to a greater degree than previously-known designs.
U.S. Pat. No. 6,682,559 to Myers, et al. also describes a valve prosthesis having an essentially tubular design. One drawback of such configurations is that relatively large horizontal forces arise along the coaptation edges of the leaflets and are transmitted to the commissural points. These forces may adversely affect the durability of the leaflets and lead to valve failure. In view of this, it would be desirable to provide a valve wherein the center of coaptation of the leaflets may be selected so as to reduce horizontal forces applied to coaptation edges of the leaflets and commissural points, thereby improving durability of the valve. In addition, it would be desirable to provide a valve design that more uniformly distributes horizontal forces over the coaptation edges of the leaflets, rather than concentrating those forces at the commissural points.
In an effort to more nearly recreate the force distribution along the leaflets of natural tissue valves, some previously-known valve designs include circular base portions having longitudinal projections that function as anchors for the commissural points, such as described in U.S. Pat. No. 5,855,601 to Bessler, et al. and U.S. Pat. No. 6,582,462 to Andersen, et al.
While the valve prostheses of Bessler and Andersen may be readily collapsed for delivery, those designs are susceptible to problems once deployed. For example, the longitudinal projections of such prostheses may not provide sufficient rigidity to withstand compressive forces applied during normal movements of the heart. Deformation of the commissural anchors may result in varied forces being imposed on the commissures and leaflets, in turn adversely impact functioning of the leaflets. In addition, because the exteriors of the foregoing valve prostheses are substantially cylindrical, the prostheses are less likely to adequately conform to, and become anchored within the valve annulus anatomy during deployment. As a result, cyclic loading of the valve may result in some slippage or migration of the anchor relative to the patient's anatomy.
In view of the foregoing, it would be desirable to provide a valve that is capable of conforming to a patient's anatomy while providing a uniform degree of rigidity and protection for critical valve components. It therefore would be desirable to provide a valve prosthesis having portions that are capable of deforming circumferentially to adapt to the shape of the pre-existing valve annulus, but which is not susceptible to deformation or migration due to normal movement of the heart. Still further, it would be desirable to provide a valve prosthesis having a multi-level component that is anatomically shaped when deployed, thereby enhancing anchoring of the valve and reducing the risk of migration and perivalvular leaks.